Fleet sales numbers are hard to find, but not impossible. I found some for the first half of 2007. Eight percent of Camries sold during that period were fleet sales. Sixteen percent of Corollas sold during that period were fleet sales. Interestingly, by taking fleet sales out of the occasion, the Corolla loses out to the Civic as the best-selling compact.
SOURCE. These numbers are not insignificant, and contradict Steve's assertions about the lack of Toyota fleet sales.
On the other hand, those numbers don't touch the Ford Crown Victoria, which, between taxis and police cruisers, had nine fleet sales for every one retail sale.